This patch switches to open device fd in net_init_vhost_vpda(). This is
used to prepare for the multiqueue support.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20211020045600.16082-2-jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>